Abstract: The development of glufosinate-resistant corn represents a new weed management system for corn growers. Field experiments were conducted from 1995 to 1997 at four locations in southwestern Ontario. The objective of this study was to determine the effect of timing of weed control relative to the growth stage of corn with glufosinate applied alone or in combination with residual herbicides. Control of all species tested improved with the addition of atrazine plus dicamba to glufosinate, applied from the two- to eight-leaf stage of corn growth. Based on a 90% weed dry matter reduction, glufosinate with atrazine plus dicamba controlled common ragweed, common lambsquarters, and pigweed species at the three-leaf stage of corn and yellow foxtail, barnyardgrass, and large crabgrass at the two-, four-, and eight-leaf stage of corn, respectively. Weed control with glufosinate alone was improved when applied at the later growth stages of corn. Glufosinate applied alone at the four-leaf stage of corn controlled common ragweed and common lambsquarters, whereas pigweed species were controlled effectively at the eight-leaf stage of corn growth. Corn grain yield was consistently higher when glufosinate was applied in combination with residual herbicides, compared to glufosinate alone. Glufosinate in combination with residual herbicides applied to corn at the three- to five-leaf stage may represent the best timing for weed control. Our data suggested that a tank mixture of glufosinate with other postemergence residual herbicides or a split application of glufosinate in combination with cultivation may be required for weed control in glufosinate-resistant corn.
Nomenclature: Atrazine; dicamba; SAN 582 (proposed name, dimethenamid), 2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-yl)-acetamide; glufosinate; metolachlor; redroot pigweed, Amaranthus retroflexus L. #3 AMARE; common lambsquarters, Chenopodium album L. # CHEAL; yellow foxtail, Setaria glauca (L.) Beauv. # SETGL; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCR; common ragweed, Ambrosia artemisiifolia L. # AMBEL; corn, Zea mays L.
Additional index words: Integrated weed management.
Abbreviations: DAE, days after emergence; DM, dry matter; HRC, herbicide-resistant crops; IWM, integrated weed management; POST, postemergence; PRE, preemergence.